Ventilation mask

ABSTRACT

A nasal mask has exhalation scoop fixed adjacent a lower portion of mask, adapted to overlie an upper lip of a patient when the mask is worn. The mask includes ports for sampling flow of CO2 expelled from the mouth and nose of the patient to the end-tidal CO2 port, and a pressure-based flow resistor for balancing flow of CO2 expelled from the mouth and the nose of the patient.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from PCT Patent Application Serial No.PCT/2017/048046, filed Aug. 22, 2017, which claims priority from U.S.Provisional Application Ser. No. 62/510,192, filed May 23, 2017, andfrom U.S. Provisional Application Ser. No. 62/467,808, filed Mar. 6,2017 and from U.S. Provisional Application Ser. No. 62/425,371, filedNov. 22, 2016 and from U.S. Provisional Application Ser. No. 62/394,405,filed Sep. 14, 2016, the disclosure of each of which is incorporatedherein by reference in its entirety.

BACKGROUND OF THE INVENTION

The present invention relates to improvements in anesthesia masks andventilation masks.

During surgery a patient usually is placed under anesthesia. The mostcommon delivery system consists of canisters containing anesthesia gasesand oxygen, a system of regulating the gas flow and the patient'sbreathing, and a device ensuring the potency of the patient's airway forbreathing, oxygenation and the delivery of the anesthetic gas mixture. Aventilation mask is used to provide oxygen to the patient either duringemergency and/or elective airway management, which includes but is notlimited to: before a patient is anesthetized for surgery; while thepatient is sedated during the surgery or procedure; while the patient isrecovering from anesthesia; after the patient has recovered fromanesthesia; and during any event where a patient requires supplementaloxygen. However, conventional ventilation masks are less than ideal.

Moreover, situations may arise during surgery that require rapidintubation of a patient. Full face masks, i.e. masks covering both thenose and mouth of a patient are problematic in emergency situationssince a mask must be removed to uncover the mouth of a patient forintubation. However, removing the mask also removes oxygen support.

In our co-pending PCT Application Serial Nos. PCT/US2014/44934,PCT/US2015/034277 and PCT/US2015/044341 (hereinafter the '934, '277 and'341 PCT applications), we provide improved ventilation/anesthesia masksthat overcome the aforesaid and other problems with the prior art byproviding, in one aspect, a combination mask comprising a nasal portionor mask and an oral portion or mask defining respectively a nasalchamber and an oral chamber, detachably connected to one another whereinthe nasal mask may be used separately or connected to the oral mask as acombination nasal/oral mask. We also provide a nasal mask with one ormore ports, and various strap systems for holding the mask on apatient's face. We also provide a nasal only mask with one or moresensors for sensing end-tidal CO₂ or other gases, and for scavenginggases. See our co-pending PCT Application Serial No. PCT/US16/037070(hereafter the '070 PCT application). Such combination nasal/oral masksand nasal only masks are available commercially from RevolutionaryMedical Devices, Inc. of Tucson, Ariz., under the trademark SuperNO₂VA®.

The present invention provides improvements in nasal masks such asdescribed in our aforesaid PCT applications, by providing an exhalationscoop adjacent the bottom of the nasal mask to overlay at least in partthe upper lip of a patient, when the mask is worn. The exhalation scoopmay be formed of a flexible, preferably resiliently deformable material,and fixed mechanically or adhesively to the mask. Alternatively, theexhalation scoop may be formed with a lip to fit in a matching groove inthe outer surface of the nasal mask, or formed integrally with the mask.The exhalation scoop is flexible so as to permit a surgeon to compressor push the exhalation scoop out of the way to permit access to thepatient's mouth, while the nasal mask remains on the patient.Alternatively, the exhalation scoop may be folded back on itself leavingaccess to the patient's mouth, while the nasal mask remains on thepatient.

In one aspect the invention provides a nasal mask having exhalationscoop formed of a the flexible or resiliently deformable material, fixedadjacent a lower portion of mask, adapted to overlie an upper lip of apatient when the mask is worn.

In another aspect the exhalation scoop is adapted to be pressed out ofthe way to permit access to the mouth of a patient.

In still another aspect the exhalation scoop is adapted to be foldedback on itself to permit access to the mouth of a patient.

In yet another aspect, the mask includes an end-tidal CO₂ port forsampling exhaled CO₂ expelled from a mouth and/or nose of a patient.

In still yet another aspect the mask includes a ventilation port adaptedto attach to an anesthesia machine, ventilation machine, hyperinflationbag or other ventilation or gas accessory.

In a still further aspect the mask further includes an oxygen portadapted for connection to an oxygen source for supplying oxygen to aninterior of the mask.

In another aspect, the mask has tabs or eyelets for attaching one ormore mask straps.

The present invention also provides a method for ventilating a patient,comprising providing a nasal mask having exhalation scoop formed of athe flexible or resiliently deformable material, fixed adjacent a lowerportion of mask, and adapted to overlie an upper lip of a patient whenthe mask is worn, and when needed, moving the exhalation scoop out ofthe way to provide access to the patient's mouth.

In one aspect of the method the exhalation scoop is pressed out of theway to permit access to the mouth of a patient.

In another aspect of the method the exhalation scoop is folded back onitself to permit access to the mouth of a patient.

In still yet another aspect the method includes providing a nasal maskwith a exhalation scoop as described above, and monitoring end-tidal CO₂port by sampling exhaled CO₂ expelled from a mouth and/or nose of apatient using an end-tidal CO₂ monitor.

In still yet another aspect, the mask is attached to an anesthesiamachine, ventilation machine, hyperinflation bag or other ventilation orgas accessory, or to an oxygen source for supplying oxygen to aninterior of the mask.

The present invention also provides a nasal mask having an exhalationscoop fixed adjacent a lower portion of the mask, adapted to overly anupper lip of a patient when the mask is worn, wherein said exhalationscoop includes an opening permitting access to a mouth of a patient whenthe mask is worn, and a flexible flap arranged on an inside surface ofthe scoop for closing off the opening. In one embodiment, the openingcomprises an aperture or one or more slits.

The invention also provides a method for ventilating a patient,comprising providing a nasal mask having an exhalation scoop fixedadjacent a lower portion of the mask and adapted to overly at least inpart the mouth of the patient when a mask is worn, wherein theexhalation scoop includes an aperture permitting access to the mouth ofthe patient, and accessing the mouth of the patient by pushing afunctional tool through the aperture.

In one embodiment, the tool is removed, the aperture is essentiallyclosed by the flap.

Also provided is a nasal mask having an exhalation scoop fixed adjacenta lower portion of the mask, adapted to overly the mouth of a patient,at least in part, when the mask is worn, said mask further including anend-tidal CO₂ port for sampling exhaled CO₂ expelled from a mouth andnose of the patient, wherein said end-tidal CO₂ port is further providedwith an interface for connecting with an interface connector.

In one embodiment, the interface connector comprises a luer lockinterface connector. Finally, the invention provides a method forventilating a patient, comprising providing a nasal mask as abovedescribed, and introducing a fluid into the interior of the mask throughthe interface connector.

In one embodiment, the fluid comprises a sedative such as lidocaine.

In another embodiment, the fluid added through the interface connectoris mixed with gases within the mask.

In yet another embodiment, the present invention provides improvementsover the nasal mask as described above, and having oral and nasal CO₂sampling ports, by providing a mechanism for substantially balancingflow between the oral and nasal CO₂ sampling ports of the mask.

More particularly, the present invention provides a pressure-based flowresistor located inside the nasal chamber of the mask for maintainingsubstantially constant flow between the nasal and oral sampling openingsby varying resistance as a function of differential pressure between thenasal and oral chambers.

In one aspect of the invention there is provided a nasal mask having anexhalation scoop fixed adjacent a lower portion of mask, adapted tooverlie an upper lip of a patient when the mask is worn, said maskincluding first port for sampling exhaled CO₂ expelled from a mouth ofthe patient, and a second port for sampling exhaled CO₂ expelled from anose of a patient, said mask further including a pressure-based flowresistor communicating with said second post adapted to maintainsubstantially constant sampling flow of CO₂ expelled from the mouth andnose of the patient to the end-tidal CO₂ port.

In still another embodiment the pressure-based flow resistor maintainsconstant flow by maintaining constant flow by varying resistance as afunction of differential pressure, between the first port and the secondport, Q_(BC), as defined by (PB−PC)^(1/2)/R_(BC).

In another aspect, the pressure-based flow resistor comprises a manifoldhaving two or more holes which communicated between a nasal chamber ofthe mask and an end tidal CO₂ port, and flow occurs due to differentialpressure between the nasal chamber and the end-tidal CO₂ port.

In yet another aspect the manifold comprises a flexible membrance thatdeflects as a function of pressure and varies the flow resistance to theend tidal CO₂ port. In such aspect the deflection amount, 6Z, preferablyvaries with resistance R_(BC), in proportion to the differentialpressure P_(B)−P_(C).

In another aspect the maximum flow resistance is defined by a geometryof a hole in the membrane that is not blocked by the membrane due to acentral opening n the membrane.

In still another aspect the membrane blocks flow to one or more holes inthe membrane when pressure deflects the membrane in the Z direction.

The present invention also provides a method for ventilating a patient,comprising providing a nasal mask having an exhalation scoop fixedadjacent a lower portion of mask, adapted to overlie an upper lip of apatient when the mask is worn, said mask including first port forsampling exhaled CO₂ expelled from a mouth of the patient, and a secondport for sampling exhaled CO₂ expelled from a nose of a patient, saidmask further including a pressure-based flow resistor communicating withsaid second post adapted to maintain substantially constant samplingflow of CO₂ expelled from the mouth and nose of the patient to theend-tidal CO₂ port, and connecting the sampling flow to an end-tidal CO₂port.

In another aspect of the method the pressure-based flow resistormaintains constant flow by maintaining constant flow by varyingresistance as a function of differential pressure, between the firstport and the second port, Q_(BC), as defined by (PB−PC)^(1/2)/R_(BC).

In still yet another aspect of the method the pressure-based flowresistor comprises a manifold having two or more holes which communicatebetween a nasal chamber of the mask and an end tidal CO₂ port, and flowoccurs due to differential pressure between the nasal chamber and theend-tidal CO₂ port.

In yet another aspect of the method the manifold comprises a flexiblemembrane that deflects as a function of pressure and varies the flowresistance to the end tidal CO₂ port. In such aspect the deflectionamount, δZ, preferably varies with resistance R_(BC), in proportion tothe differential pressure P_(B)−P_(C).

In still yet another aspect of the method the maximum flow resistance isdefined by a geometry of a hole in the membrane that is not blocked bythe membrane due to a central opening n the membrane.

In yet another aspect of the method the membrane blocks flow to one ormore holes in the membrane when pressure deflects the membrane in the Zdirection.

Further features and advantages of the present invention will be seenfrom the following detailed description, taken in conjunction with theaccompanying, wherein

FIGS. 1A-1D are front, rear, top and perspective views respectively, ofa nasal mask incorporating an exhalation scoop in accordance with afirst embodiment of the present invention;

FIG. 2 is a perspective view showing nasal mask with an exhalation scoopin accordance with the present invention on a patient;

FIG. 3 is a view similar to FIG. 2, showing the exhalation scoopcompressed or pushed out of the way to provide oral access;

FIG. 4 is a view similar to FIG. 2, showing a nasal mask with anexhalation scoop folded out of the way to provide oral access;

FIG. 5 is a perspective view of a nasal mask with an exhalation scoopshowing an alternative method of gaining access to the mouth inaccordance with a second embodiment of the present invention;

FIG. 6 is a view similar to FIG. 5 showing how oral access is achievedusing the exhalation scoop of FIG. 5;

FIG. 7 is a view similar to FIG. 5 of a third embodiment of theinvention;

FIGS. 8A, 8B and 8C are perspective views similar to FIG. 2 of yetanother and fourth embodiment of the invention;

FIG. 9 is a side elevational view, in cross section, of the CO₂ samplingport of the FIG. 2 mask;

FIG. 10 is a side elevational view, in cross section, of the mask inFIG. 2;

FIG. 11 is a fluid flow schematic in accordance with the FIG. 2 mask;

FIG. 12A is a perspective view, from the inside, of a mask in accordancewith a preferred embodiment of the present invention;

FIG. 12B is an enlarged view of a flexible seal flap valve of the nasalmask of FIG. 12A;

FIG. 12C is a side elevational view, in cross section, of the nasal maskof FIG. 12A;

FIG. 13A is a side elevational view, in cross section, of the seal ofFIG. 12B in an open position; and

FIG. 13B is a view, similar to FIG. 13A, of the seal flap valve of FIG.13A.

As used herein “nasal mask” preferably comprises a nasal mask similar tothe nasal mask such as described in our aforesaid '934, '277, '341, and'070 PCT Applications including in particular a SuperNO₂VA® nasal maskavailable commercially from Revolutionary Medical Devices, Inc. ofTucson, Ariz.

FIGS. 1A-1D are front, rear, top and perspective views of a nasal mask10 somewhat similar to the nasal mask described in FIGS. 16A-16E ouraforesaid PCT Application No. PCT/US16/37070, but having an exhalationscoop 12 formed of a flexible, preferably resiliently deformablematerial, fixed to a lower portion 14 of the mask. Exhalation scoop 12preferably has a 00 Durometer Hardness of 0020 to 0050, to a Shore AHardness of 2-10, more preferably a Shore A Hardness of 3-7, mostpreferably a Shore A Hardness of about 5. The softer the material thebetter.

Referring also to FIG. 2, the mask 10 also includes a gas samplingdevice (shown in phantom at 16) adapted for suction attached to anend-tidal (“ET”) CO₂ port 18 and adapted for drawing gas samples fromboth the oral and nasal exhalations of the patient. One opening 20 ofthe EtCO₂ manifold is located behind the exhalation scoop 12 to overliethe upper lip of a patient, when the mask is worn by a patient, on theexterior of the nasal mask 10, where a negative pressure (pressure lessthan atmospheric pressure) is created by a gas sampling device 16. Asecond opening 22 of the manifold is located to underlie the nares ofthe patient, on the interior of the nasal mask where a negative pressureis also created by the gas sampling device 16. When the patient exhales,oral and nasal exhalation are collected through openings 20, 22 andproceed through the manifold and exit the EtCO₂ port that is connectedto the gas sampling device 16 that provided the negative pressure.Concentration levels of the gas, such as CO₂ are then measured by gassampling device 16.

The nasal mask interior chamber is pressurized through a ventilationport 23 by an anesthesia machine or another ventilation device (shown inphantom at 24). Flow from the patient's nose is drawn to the negativepressure of the opening of the manifold interior of the nasal chamber.The patient's mouth is at atmospheric pressure and the flow of the oralexhalation is channeled by the exhalation scoop where it is drawn by thenegative pressure presented by gas sampling system through the manifoldopening. Samples of both the nasal and oral exhalation flow through amanifold, and exit the EtCO₂ port 18 to the gas sampling device 16. Themask 10 also includes an oxygen port 25 for supplying oxygen from anoxygen source (shown in phantom at 27) to a patient.

One benefit of the flexible exhalation scoop design is that if thesurgeon requires access to the patients mouth to employ a device such asan intubation tube or endoscope 26, the exhalation scoop 12 can beflexed or pushed by the device in the nominal “y” direction, providingaccess to the patient's mouth as shown in FIG. 3.

Another benefit of one flexible exhalation scoop 12 design is that ifthe surgeon requires access to the patient's mouth, there exists abi-stable condition where the scoop 12 overlies the upper lip and/ormouth of the patient, as shown in FIG. 2, or the scoop 12 can be foldedover itself about the nominal “X” axis and remain stable with the scoop12 no longer covering the mouth as shown in FIG. 4. This allows accessto the patient's mouth as shown, and nasal Et CO₂ can still becollected. Once the endoscope 26 or other device is removed from thepatient's mouth, should the clinician decide to continue collecting oralEt CO₂ samples, the flexible exhalation scoop 12 can be unfolded aboutthe “X” axis, again covering the patient's mouth as in FIG. 2.

Completing the nasal mask are tabs and/or eyelets 30 for attaching oneor more head straps (not shown).

Referring to FIGS. 5 and 6, in an alternative embodiment of theinvention, the exhalation scoop 12A includes a circular aperture 50covered by a flap 52 attached to the inside of the exhalation scoop 12Aat anchor 54. Exhalation scoop 12A is similar in shape to the exhalationscoop 12 of FIGS. 1-4, but need not be made of as flexible materials.Flap 52 and anchor 54 are shown in phantom since they are on the insideof scoop 12A. Flap 50 is in a normally closed position, and is heldagainst the inside surface of scoop 12A by positive pressure within themask, when the mask is worn by a patient.

FIG. 6 shows a functional device such as an intubation tube or endoscope26 inserted through aperture 50, pushing flap 52 aside whereby to permitaccess to the patient's mouth, while permitting continual end-tidalsampling, etc. Flap 50 is flexible so as to substantially seal aroundthe functional device. When the functional tool 26 is removed, theaperture 50 is again sealed by flap 50.

In another embodiment, shown in FIG. 7, aperture 50 is replaced by aslip 70 which is backed by flexible flap 72 anchored at 74 to the insideof the exhalation scoop 12B. Similar to port 50, slit 70 permitsinsertion of a functional device through the exhalation scoop, givingaccess to the patient's mouth, while leaving the exhalation scoop inplace so as to permit continued end-tidal CO₂ sampling, etc.

Note with respect to the embodiments of FIGS. 5-6 and 7, any geometricshape may be used for the aperture, the slits and the flap so as topermit passage of a laryngoscope, endotracheal tube, endoscope or otherfunctional device to pass through the exhalation scoop, while leavingthe exhalation scoop in place for continued end-tidal CO₂ monitoring,etc. Due to the flexibility of the flap, the flap essentially sealsaround the functional tool and allows for continued collection of orallyexpelled CO₂. When the tool is removed from the scoop, the flap againcloses off the aperture or slits.

Yet another embodiment of the invention is shown in FIGS. 8A-8C. In thislatter embodiment, the Et CO₂ port has a luer connection 80, thusproviding the Et CO₂ port the ability to interface with other devices,having a luer interface connection 82 such as a syringe 84. Thus, the EtCO₂ port can be utilized to deliver fluids, or gases, includingsedatives such as lidocaine, contained in a syringe. FIGS. 8A-8B show afluid-filled syringe 84 being connected to the Et CO₂ port and FIG. 8Cshows the syringe 84 being compressed, with the fluid being expelledinto the interior of the mask. Gasses, such as O₂, that flow througheither the O₂ port, the ventilation port 86, or both, will mix with theexpressed fluid, nebulizing it where it is then inhaled by the patient.

Referring again to FIG. 2, as noted supra, mask 10 also includes a gassampling device (shown in phantom at 16) in the form of suction attachedto an end-tidal (“ET”) CO₂ port 18 and adapted for drawing gas samplesfrom both the oral and nasal exhalations of the patient. One opening 20of the EtCO₂ manifold is behind the exhalation scoop 12 to overlie theupper lip of a patient, when the mask is worn by a patient, on theexterior of the nasal mask 10, where a negative pressure (pressure lessthan atmospheric pressure) is created by gas sampling device 16. Asecond opening 22 of the manifold is below the nares on the interior ofthe nasal mask where a negative pressure is also created by the gassampling device 16. When the patient exhales, oral and nasal exhalationare collected through openings 20, 22 and proceed through the manifoldand exit the EtCO₂ port that is connected to the gas sampling device 16that provided the negative pressure. Concentration levels of the gas,such as CO₂ are then measured by gas sampling device 16.

Referring also to FIGS. 9-11, in use oral exhalation enters the CO₂ portthrough a single opening, hole 20, and nasal exhalation enters the CO₂port through a single opening, hole 30, as shown in FIG. 2. The CO₂ portis connected to a CO₂ monitoring device that creates suction, collectingthe exhalation sample by a sampling line. The mask operates in anunpressurized configuration here oxygen is supplied through the O₂ port25 and the ventilation port 23 is open to the atmosphere where both theoxygen and exhalation of CO₂ escape, as well as a pressurizedconfiguration where the oxygen enters the mask through the ventilationport and also, optionally, the oxygen port. Exhalation of the CO₂ andoxygen then exits through the ventilation port 23 that is connected toeither an anesthesia machine, a ventilator, a CPAP machine or aventilation bag such as one on a hyperinflation system.

Volumetric flow through a pipe, Q, is governed by the fluid dynamic lawsshown in

Equations 1-5.

Q=πϕ ² V/4  Eq. 1

ΔP=ρfLV ²/2ϕ  Eq. 2

ΔP=(8ρfL/π ²ϕ⁵)Q ²  Eq. 3

R ²=(8ρfL/π ²ϕ⁵)  Eq. 4

Q=ΔP ^(1/2) R  Eq. 5

wherein:Q=Volumetric flow rate (m³/min)ρ=fluid density (kg/m³)ϕ=pipe diameter (m)V=fluid velocity (m/min)ΔP=Differential pressure between two points (Pa)f=friction factor for pipeL=pipe length (m)R=pipe resistance (Pa^(1/2)-min/m³)

The fluid flow model for the current mask 10 shown in FIGS. 2 and 9-11has 4 node points with respective pressure and flow rates defined asfollows:

Node point A, Entrance of hole 20 that is the oral opening into the CO₂Port.

-   -   Hole 20 diameter, ϕ_(a)=ϕ_(CO2 Port)    -   Pressure at hole 20, P_(A)    -   Volumetric oral exhalation flow through hole 20, Q_(AC)    -   Pipe resistance from Node A to Node C, R_(AC)    -   Length of pipe from Node A to Node C, L_(AC)        Node point B, Entrance of hole 22 that is the nasal opening into        the CO₂ Port.    -   Hole 22 diameter, ϕ_(b)    -   Pressure at hole 22, P_(B)    -   Volumetric nasal exhalation flow through hole 22, Q_(BC)    -   Pipe resistance from Node B to Node C, R_(BC)    -   Length of pipe from Node B to Node C, L_(BC)        Node point C, Interior of CO₂ Port adjacent to exit of hole 22        into CO₂ Port    -   CO₂ Port diameter, ϕ_(CO2 Port)    -   Pressure at Node C, P_(C)    -   Volumetric flow through Node C, Q_(CD)    -   Pipe resistance from Node C to Node D, R_(CD)    -   Length of pipe from Node C to Node D, L_(CD)        Node point D, Exit of CO₂ Port (Connects to CO₂ Sample line)    -   CO₂ Port diameter, ϕ_(CO2 Port)    -   Pressure at Node D, P_(D)    -   Volumetric flow through Node D, Q_(CD)        Flow between each of the Node points is defined as follows:

Q _(AC) +Q _(BC) =Q _(CD)  Eq. 6

Q _(AC)=(P _(A) −P _(C))^(1/2) /R _(AC)  Eq. 7

Q _(BC)=(P _(B) −P _(C))^(1/2) /R _(BC)  Eq. 8

Q _(CD)=(P _(C) −P _(D))^(1/2) /R _(CD)  Eq. 9

Ideally, the flow from the oral and nasal exhalation, Q_(AC) and Q_(BC),are equal in order to measure exhaled CO₂. In an unpressurizedconfiguration, P_(A) and P_(B) are both approximately equal and equal tothe atmospheric pressure. In such configuration, the associatedresistance between nodes, R_(AC) and R_(BC) would be designed to beequal by properly configuring the associated pipe diameters and pipelengths. The challenge is that in a pressurized configuration, the nasalportion of the mask, PB, is pressurized to a nominal value of 10-15 CMH₂O relative to the atmosphere and P_(A). In such configuration, R_(BC)will need to be proportionally larger than R_(AC) in order to haveQ_(AC) equal Q_(BC). If R_(BC) were not increased, the Q_(BC) would belarger than Q_(AC). In order to maintain substantially equal oral andnasal flow for CO₂ sampling for both the unpressurized and pressurizedconfigurations, R_(BC) must vary as a function of P_(B) in order tomaintain equal flow.

As used herein the terms “substantially balancing flow” and“substantially constant flow” are used interchangeably, and mean a flowof within about volume 10%, preferably within about volume 5%, morepreferably within about volume 2-3%.

A preferred embodiment of a pressure-based flow resistor is illustratedin FIGS. 12A-12C. In this embodiment, the nasal mask 100, which issimilar to mask 10 described above, includes a manifold 102 with two ormore holes 104, 106 connecting nasal chamber of the mask to a CO₂ port18. Referring also to FIGS. 13A and 13B a membrane disk 112 having anopening 114 is aligned over a hole 116 which covers the manifold 102where under a given pressure, P_(B), nasal exhalation can travel throughthe hole 114 of the manifold, hole 116, as well as a hole 118 into theCO₂ port 18. As pressure increases, to P_(BCrit), the membrane disk 112deflects in the Z direction by moving up by a distance δZ. At thatpoint, flow from the nasal chamber 11 to hole 118 is blocked and canonly travel through hole 116. As a result, flow resistance from thenasal chamber 11 to the CO₂ port 18 R_(BC), is increased. Hole 118 andhole 116 geometry can be selected so that when the membrane disc 112 hasdeflected an amount less than δZ, the flow, Z_(BC), as defined by(PB−PC)^(1/2)/R_(BC) is nominally constant and made substantially equalto Om from Oral exhalation. As a result, sampling flow is substantiallyequalized.

Various changes may be made in the above without departing from thespirit and scope of the invention.

What is claimed:
 1. A nasal mask comprising: an inner surface forming anasal chamber; a ventilation port that extends from an upper portion ofthe nasal mask in a first direction; an end-tidal CO₂ port that extendsfrom an upper portion of the nasal mask and comprises an openingadjacent a lower portion of the nasal mask; and an exhalation scoopfixed adjacent a lower portion of the nasal mask and adapted to overliean upper lip of a patient when the mask is worn; wherein the opening islocated behind the exhalation scoop for sampling CO₂ expelled from themouth of the patient, and the exhalation scoop is formed of a materialthat is flexible relative to a material of the nasal mask such that theexhalation scoop is adapted to be folded back in the first directiontoward the nasal chamber to permit access to the mouth of the patient.2. The nasal mask of claim 1, wherein the end-tidal CO₂ port extendsfrom the upper portion of the nasal mask in the first direction.
 3. Thenasal mask of claim 1, wherein the end-tidal CO₂ port comprises anotheropening located in the nasal chamber to underlie a nare of the patientfor sampling exhaled CO₂ expelled from a nose of the patient.
 4. Thenasal mask of claim 1, wherein the ventilation port is configured toconnect with any of an anesthesia machine, a ventilation machine, and/ora hyperinflation bag.
 5. The nasal mask of claim 1, further comprisingan oxygen port configured to connect with an oxygen source for supplyingoxygen to the nasal chamber.
 6. The nasal mask of claim 1, wherein theoxygen port extends from the upper portion of the nasal mask in thefirst direction.
 7. The nasal mask of claim 1, wherein the material ofthe exhalation scoop is formed of a material having a Shore 00 DurometerHardness of 0020 to
 0050. 8. The nasal mask of claim 1, wherein thematerial of the exhalation scoop is formed of a material having a ShoreA Hardness selected from 2-10 or 3-7.
 9. The nasal mask of claim 1,further comprising a groove in an outer surface of the nasal mask,wherein the exhalation scoop comprises a lip configured to fit in thegroove.
 10. The nasal mask of claim 1, wherein the exhalation scoop isintegrally formed with the nasal mask.
 11. The nasal mask of claim 1,wherein the exhalation scoop is configured to be folded around an axisthat extends in a second direction, and wherein the second direction istransverse relative to the first direction.
 12. The nasal mask of claim1, wherein the exhalation scoop comprises an opening configured topermit access to the mouth of the patient when the mask is worn.
 13. Thenasal mask of claim 12, wherein the exhalation scoop comprises aflexible flap arranged on an inner surface of the exhalation scoop forclosing off the opening.
 14. The nasal mask of claim 12, wherein theopening comprises any of an aperture and one or more slits.
 15. A methodfor ventilating a patient, comprising: providing a nasal mask having aninner surface forming a nasal chamber, a ventilation port that extendsfrom an upper portion of the nasal mask in a first direction, anend-tidal CO₂ port that extends from an upper portion of the nasal maskand comprises an opening adjacent a lower portion of the nasal mask, andan exhalation scoop fixed adjacent a lower portion of the nasal mask andadapted to overlie an upper lip of a patient when the mask is worn, suchthat the opening is located behind the exhalation scoop; connecting theventilation port to any of an anesthesia machine, a ventilation machine,and/or a hyperinflation bag; folding the exhalation scoop back in thefirst direction toward the nasal chamber to permit access to the mouthof the patient; and monitoring end-tidal CO₂ by sampling exhaled CO₂expelled from the mouth of the patient into the opening.
 16. The methodof claim 15, monitoring end-tidal CO₂ by sampling expelled from a nareof the patient into another opening of the end-tidal CO₂ port located inthe nasal chamber.
 17. The method of claim 15, further comprisingconnecting an oxygen port of said nasal mask to an oxygen source forsupplying oxygen to the nasal chamber of the nasal mask.
 18. The methodof claim 15, wherein folding the exhalation scoop back in the firstdirection comprises folding the exhalation scoop around an axis thatextends in a second direction, and wherein the second direction istransverse relative to the first direction.
 19. The method of claim 15,further comprising unfolding the exhalation scoop in the seconddirection away from the nasal chamber to permit access to the mouth ofthe patient, wherein the second direction is opposite to the firstdirection.
 20. The method of claim 15, further comprising connecting theend-tidal CO₂ port of the nasal mask to a gas sampling device.